The reinforcement of rock originally involved the use of passive support systems that utilized timber and steel structural supports. Active support systems were subsequently developed including the provision of relatively rigid roof bolts that have been widely used and still find application. Early roof bolts were provided with mechanically operated wedge devices to facilitate anchorage of the roof bolts in the relevant rock. Later, concrete grout and chemical anchoring materials were developed for anchorage of roof bolts. Most recently, flexible wire tendons or cable bolts have found widespread application and are commonly used with such anchoring materials. The cable bolts usually have spaced apart cage sections along their length where the plurality of wires that make up the cable bolt are spread apart to assist in permitting the anchoring material to grasp the cable bolt.
To install such a wire tendon, the bore for receipt of the tendon is first drilled into the rock to be supported. Given the length of the tendon, it is common to use a number of drill rod extensions to obtain the required bore depth. The selected anchoring material is then inserted in the bore and the wire tendon manually or mechanically driven into the bore prior to being tensioned to thereby support the rock once it has been anchored in position by the anchoring material.
The anchoring material is typically contained in a cartridge that facilitates its insertion into the drilled bore. The material exists in the cartridges as separate adhesive and catalyst components that are mixed together by the tendon, when inserted in the bore, to cause the anchoring material to set and so anchor the tendon in position.
A cable bolt can be up to 10 meters long and weigh up to 32 kilograms. Currently an operator has to feed the cable bolt by hand. It has been highlighted by mine managers that this is a significant health and safety concern due to the difficulty and regularity of the process, and can lead to a possible injury. Also, there is a possibility for the cable bolt to fall on the operator as it is being fed into the drilled hole.
Below is a typical cable bolting procedure.
1. Drill:
Insert a first drill steel component (with cutter at top) into square chuck in rotation unit of a drill rig, drill up (with washer plate used for aligning), and clamp when at full travel, retract drill unit and load extension drill segment, spin and feed (ensuring that the threads engage). Continue process until all needed segments are used and then remove drill segments with same procedure in reverse.
2. Load Chemicals:
Slide a one-way catch device over a first chemical sausage. Push chemical up hole with a flexible plastic rod (pusher) to the top of the hole. Load a second chemical with catch device up to meet the first at the top of the hole. And then continue until the drilled hole is filled.
3. Load Cable bolt:
Manually push cable bolt up hole by hand and then load the free end into the drill rig rotation unit.
4. Mix Chemical:
Feed the cable bolt up and then spin, stopping the feed when the cable bolt reaches the top of the hole, but continue to spin for 10 seconds or so to mix chemicals.
5. Tension Cable bolt:
Retract the stab-jack. Insert a tension collar and grout pipes through washer plate. Lift tensioner and attach to end of cable bolt.
Activate tensioner.
6. Grout at a later time.